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Date: Thu, 14 Sep 2023 09:56:57 +0200
From: Christian Brauner <brauner@kernel.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>, Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
	Fenghua Yu <fenghua.yu@intel.com>,
	Reinette Chatre <reinette.chatre@intel.com>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>,
	Tejun Heo <tj@kernel.org>,
	Trond Myklebust <trond.myklebust@hammerspace.com>,
	Anna Schumaker <anna@kernel.org>, Kees Cook <keescook@chromium.org>,
	Damien Le Moal <dlemoal@kernel.org>,
	Naohiro Aota <naohiro.aota@wdc.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-s390@vger.kernel.org, linux-rdma@vger.kernel.org,
	linux-nfs@vger.kernel.org, linux-hardening@vger.kernel.org,
	cgroups@vger.kernel.org
Subject: Re: [PATCH 03/19] fs: release anon dev_t in deactivate_locked_super
Message-ID: <20230914-zielt-einzog-00389009b293@brauner>
References: <20230913111013.77623-1-hch@lst.de>
 <20230913111013.77623-4-hch@lst.de>
 <20230913232712.GC800259@ZenIV>
 <20230914023705.GH800259@ZenIV>
 <20230914053843.GI800259@ZenIV>
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In-Reply-To: <20230914053843.GI800259@ZenIV>

> BTW, this part of commit message in 2c18a63b760a is rather confused:
>     Recent rework moved block device closing out of sb->put_super() and into
>     sb->kill_sb() to avoid deadlocks as s_umount is held in put_super() and
>     blkdev_put() can end up taking s_umount again.
> 
> That was *NOT* what a recent rework had done.  Block device closing had never
> been inside ->put_super() - at no point since that (closing, that is) had been
> introduced back in 0.97 ;-)  ->put_super() predates it (0.95c+).

I think the commit message probably just isn't clear enough. The main
block device of a superblock isn't closed in sb->put_super(). That's
always been closed in kill_block_super() after generic_shutdown_super().

But afaict filesystem like ext4 and xfs may have additional block
devices open exclusively and closed them in sb->put_super():

xfs_fs_put_super()
-> xfs_close_devices()
   -> xfs_blkdev_put()
      -> blkdev_put()

ext4_put_super()
-> ext4_blkdev_remove()
   -> blkdev_put()